1. Field of the Invention
This invention relates to a method and apparatus for detecting and quantizing the phase of high harmonics components in sine wave synthesis encoding.
2. Description of the Related Art
There are known a variety of encoding methods for audio signals (inclusive of speech and acoustic signals) in which the signals are compressed by exploiting statistic properties in the time domain and in the frequency domain of the audio signals and psychoacoustic characteristics of the human being. These encoding methods may be roughly classified into time-domain encoding, frequency domain encoding and analysis-synthesis encoding.
Examples of the high efficiency encoding of speech signals etc include sinusoidal coding, such as harmonic encoding, multi-band excitation (MBE) encoding, sub-band coding, linear predictive coding (LPC), discrete cosine transform (DCT) encoding, modified DCT (MDCT) encoding and fast Fourier transform (FET).
Meanwhile, in high efficiency speech coding, employing the above-mentioned MBE encoding, harmonics encoding or sinusoidal transform coding (STC) for input speech signals, or employing the sinusoidal coding for linear prediction coding residuals (LPC residuals) of input speech signals, the information concerning the amplitude or the spectral envelope of respective sine waves (harmonics) as elements of analysis/synthesis is transmitted. However, the phase is not transmitted and simply the phase is calculated suitably at the time of synthesis.
Thus, a problem is raised that the speech waveform, reproduced on decoding, differs from the waveform of the original input speech waveform. That is, for realizing the replica of the original speech signal waveform, it is necessary to detect the phase information of the respective harmonics components frame-by-frame and to quantize the information with high efficiency to transmit the resulting quantized signals.